conceivable needs much farther into the future. The prospects are less clear for copper, lead, zinc, and many minor metals because of the conditions of occurrence and lack of adequate data on deposits already discovered. Of all metals and several important nonmetals, however, adequate supplies at present costs will be dependent—in the future as they have been in the past— on new ore discoveries, continued technological advance, and maintaining a world trading and investment system that enables the countries lacking particular mineral resources to draw upon those which have them. Advancing technology and changes in the relative prices of different metals will no doubt bring about substitutions of one metal for another, and of plastics and other more abundant materials for metals. These shifts will help prevent severe shortages. If price rises occur, they can be met by increased recycling of junk materials and other conservation measures that have a large potential for increasing the life of ore reserves. Although the ultimate depletion of mineral reserves is theoretically inevitable, it is very difficult to say anything scientific about the prospects. For most minor minerals, data on reserves is extremely meager. For the major minerals, total depletion will come only after the world has changed so much in technology and culture that any forecast by the present generation would probably be irrelevant. Forest Products Of the major raw materials, our indicators of scarcity register grounds for apprehension and concern only for forest products, especially saw timber. The world will probably want a doubling or more by the year 2000. This may strain the world's capacity to produce, so that prices for timber products will force an even greater resort to substitute materials and unexploited forest zones than we have so far seen. However, the U.N. Food and Agriculture Organization (FAO) data indicate that half the world's output of saw logs and 37 percent of its total wood came from northern America and Europe in 1965, although forest acreage in these two areas was only 22 percent of the world's total. If other forested areas can be brought into more intensive production, the future situation could be greatly eased. Tropical hardwoods and the introduction of faster growing species, including hybrids, in other areas are large potential resources. They would add a bit of optimism to the picture, as would improvements in cutting and management practices in many parts of the world. Water Supplies The outlook for water supplies is difficult to assess on a world scale because of lack of statistical information on which to base projections. Furthermore, water statistics by countries or world regions mean very little;ulture" in 1966 were taken from the U.N. F'ood and Agriculture Organization's Production Yearbook 1967 (7, Tables 143-148), although in most cases they appeared to be incomplete.